Birth weight correlates with size but not shape of the normal human placenta.

INTRODUCTION: Studies on developmental programming rely on various measures of size and form of the human placenta. Size and form are not independent of each other and covariation patterns were not determined systematically.
METHODS: Twenty-two morphologic parameters were determined on 418 placentas from uncomplicated singleton pregnancies. We determined (i) placenta weight and birth weight, (ii) form parameters such as diameters, thickness, roundness, and eccentricity of cord insertion, and (iii) shape variability by geometric morphometry. Geometric morphometry analyzes shape variability independent of size. We define the technical terms form and shape according to the language of geometric morphometry.
RESULTS: Placenta weight correlated with birth weight. The form parameters correlated variably with placenta weight and shape. Shape variability did not correlate with birth weight and placenta weight. DISCUSSION AND
CONCLUSIONS: The correlation of placenta weight with birth weight stays a cornerstone of prenatal programming. Shape analysis shows that form parameters are hybrids of size and shape. Shape variability can be interpreted as an outcome of adaptation of a placenta to maternal factors and the associated uterine habitat. Correlation analysis of the whole data array provides a rigorous statistical frame to interpret published data and plan new studies.